Accurate in-vivo measurement of human corneal thickness (pachymetry) is an important diagnostic procedure in ophthalmology. Pachymetry is an important precursor to refractive surgery procedures such as LASIK, where the corneal thickness determines the appropriate flap thickness setting and sets the upper limit for laser ablation. The recently published NEI-sponsored Ocular Hypertension Treatment Study (OHTS) found that corneal thickness is just as important as intraocular pressure as a risk factor for the development of glaucoma. As a results of OHTS, pachymetry has become a standard part of the clinical examination for ocular hypertensives and other glaucoma suspects. A new generation of optical pachymeters based on low-coherence interferometry (similar to optical coherence tomography or OCT) is poised to bring the benefits of higher resolution as well as noncontact measurement to pachymetry. This Phase I Small Business Innovative Research application proposes to develop new technology, which will significantly advance optical pachymetry by use of a novel, common-path spectral interferometric system design which delivers ease of use (hand-held or slitlamp-mounted probe, reduced constraints on axial positioning) and high resolution (projected <3 p.m repeatability) in a robust and inexpensive package (no moving parts, projected cost <$10K/unit). Our team of investigators includes experts in optoelectronic device characterization and manufacturing, as well as our consultants who include academic and clinical pioneers in OCT technology development and applications in retinal and anterior segment imaging. The specific aims of the proposal are to: 1. Construct a novel common-path spectral interferometric optical pachymeter engine featuring high resolution (<3 microns repeatibility) and high scan rate (20 Hz), with robust and inexpensive components; 2. Design and construct two handheld pachymeter probe prototypes suitable for evaluation for glaucoma, presurgical, and intra-surgical applications; 3. Develop user-friendly software enabling automatic A-scan capture and corneal thickness calculation; 4. Demonstrate pachymeter operation in calibrated reference reflectors and two eye bank eyes in vivo, and provide a prototype device to our clinical consultant for in vivo testing under separate NIH support.